This invention relates to AMTI synthetic aperture radar systems, and in particular to means for improving the slowly moving target detection capability of such systems.
Stationary and slowly moving targets that are concealed in foliage often go undetected by conventional airborne radar systems. This is especially true of targets whose clutter spectrum is within that of the ground clutter spectrum seen by the aircraft radar. Clutter reduction using multiple element physical antenna arrays is virtually impossible due to the antenna size required for operation in a suitable frequency range (20 - 200 MHz, for example). Furthermore, the use of physical antenna arrays for clutter reduction implies the use of exactly matched antenna elements.
The locating and tracking of moving targets in ground clutter by an airborne synthetic aperture radar system has been disclosed by Sletten et al in U.S. Pat. No. 3,735,400 issued May 22, 1973. Such a system, however, employs very complex circuitry and requires signal filtering by a multiplicity of narrow band channels and the integrating of many echoes following each filter in order to achieve effective antenna gain and signal directivity. Although radar systems of the type disclosed by Sletten et al provide improved target detection capabilities, there yet remains the need for more effective, simplified systems that can operate in a monopulse mode and that can simultaneously detect various targets travelling at different velocities. The present invention is directed toward satisfying such a need.